Release 3.11.3

Fixed

• Fix cases in new emphasis handling that did not handle long chains of tokens
  like they should (#1690).
• Fix quadratic-time parsing of many consecutive reference definitions, and of
  many consecutive footnote definitions in the footnotes extension.
• Support automatic links with URL schemes other than HTTP and FTP, such as
  <ssh://example.org> (#1244).
• Fix quadratic-time id generation in the toc extension when many headers
  share the same text.
• Ignore glossary abbreviations with empty definitions after inline elements,
  consistently with abbreviations before inline elements.
• Strip complete HTML tags with quoted > characters from toc labels and
  generated heading IDs.
• Fix quadratic-time regex backtracking in attr_list when a block ends with an
  unclosed attribute list followed by a long run of spaces, e.g. a line
  consisting only of { and some text with many trailing spaces (#1656).
• Fix quadratic-time regex backtracking in hash headers when a long run of #
  characters is followed by more text on the same line.
• Fix quadratic time when a document contains many unclosed HTML comments (<!--
  with no matching -->).
• Fix regression in BacktickInlineProcessor where text could be lost when opening
  and closing backticks did not match (#1668).
• Escape the language name in the codehilite extension's non-Pygments output to
  maintain consistency with Pygments output.
• Preserve attributes without a value in the attr_list extension exactly as
  provided, rather than rendering them as key="key", so the same source
  renders consistently under both the html and xhtml output formats
  (#1501).